Fuel control systems are known for motor vehicle engines which compensate for fuel delay caused by slow fuel vaporization during cold engine operation by utilizing predetermined compensation values to alter the amount of fuel injected. The compensation values are stored in tables contained in an electronic engine controller which implements the fuel control system. As the engine warms up, different values are utilized to reflect the increased fuel vaporization rate. Such values are typically stored as a function of engine coolant temperature which correlates generally with the temperature of engine components contacted by fuel as it is injected and hence correlates generally with fuel vaporization rate. The compensation values can be obtained from a delay model which predicts the mass of fuel on the interior surface of the induction system of the engine for a particular engine coolant temperature and which also predicts a time constant indicative of a rate with respect to time at which fuel leaves the interior surfaces of the induction system for a particular engine coolant temperature. The delays result in a momentary lean air/fuel condition during acceleration and a momentary rich air/fuel condition during deceleration.
Known methods of generating the delay model involve an iterative trial-and-error process of generating a model, generating compensation values from the model, operating and monitoring the engine using the values, and subsequently altering the model or the values to cure observed deficiencies in engine operation. Such known methods are time consuming and may not result in an optimal fuel control strategy.
Accordingly, there exists a need for an improved method of generating compensation values for use by a fuel control system in compensating for fuel delay caused by slow fuel vaporization during cold engine operation.